Method of producing columbium and tantalum



Dec. 12, 1961 R. A. Foos ETAL 3,012,877

METHOD OF PRODUCING COLUMBIUM AND TANTALUM Filed June 20, 1958 STORAGESTORAGE 1. (X1 fix) FEEDER 46 FEEDER l2 l5 PULVERIZER l8 I /HOP7PER I9 dHOJRPER FEEDER 8 9 25 EXTRUDER rS21-1. 4 24 REACTOR" RAYMOND A. FOOSROBERT L.MADDOX INVENTORS SALT BATH FURNACE United States Patent3,012,877 METHOD OF PRODUCING COLUMBIUM AND TANTALUM Raymond A. Foos andRobert L. Maddox, Cincinnati, Ohio, assignors to National Distillers andChemical Corporation, New York, N.Y., a corporation of Virginia FiledJune 20, 1958, Ser. No. 743,410 8 Claims. (Cl. 75-84.4)

This invention relates to a new and improved process for the preparationof metals. More particularly, the invention pertains to a continuousprocess for the production of columbium and tantalum metals and mixturesthereof by reduction of the double fluoride salts of these metals.

In recent years there has been considerable interest in the productionof high purity columbium and tantalum metals. Many of the processesheretofore proposed for commercial application first prepare the doublefluoride salts of these metals, and then subject these salts to areduction treatment in order to yield the desired metal product. Forexample, in one process directed to the preparation of columbium ortantalum metals the double fluoride salts have been electrolyticallyreduced. This process is, however, quite costly, and many of therecently proposed processes attempt to provide more economical methods.One such method is the chemical reduction of the double fluoride saltswith known reducing agents such as metallic sodium, etc. However, thismethod has the disadvantage of being essentially a batch-type operationwhich requires elaborate reactor preparation and spalt removal systems.

It is one object of this invention to provide a process for recoveringthe metals from their double fluoride salts which avoids the problemsencountered in the prior art methods. Another object of this inventionis to provide a chemical reduction process which can be operatedcontinuously independent of scale with the production of outstandingyields of high quality metal products.

These and other objects of the invention are attained by utilizing acarefully controlled reduction process involving the reaction of thedouble fluoride salts of columbium and tantalum with a reducing agentunder prescribed operating conditions. In general, the process comprisesthe steps of comminuting or pulven'zing the double fluoride saltreactant, degassing and dehydrating the comminuted salt and then mixingthe so-treated salt with a molten reducing agent such that all reactantsare contacted in a liquid media under certain specific conditions toeifeot a continuous reduction reaction with continuous recovery offinely divided metal product. In accordance with another aspect of thisprocess, an alkali metal halide salt may be comminuted along with thedouble fluoride salt to ensure the production of high yields of qualitymetal. Other important features of the invention will be described indetail hereinafter.

The double fluoride salts which may be employed in the process of thisinvention will correspond to the following structural formula:

ductant is especially preferred. In carrying out the reduction of thedouble fluoride salt, it is desirable to control the amount of reducingagent employed to ensure I ice that substantially stoichiometric amountsare fed into the reaction zone. In accordance with the preferredoperation, a small excess of the reducing agent is employed.

The inert salt diluent which may be employed in conjunction With'thedouble fluoride salt reactant can be an alkali metal halide salt such assodium and potassium chlorides, bromides and iodides. The amount ofdiluent salt utilized is not critical, though preferably a 1:1 ratio ofdiluent salt to double fluoride will be provided.

For a more complete understanding of this invention, reference will nowbe made to the drawing which is a schematic showing of one form of theapparatus wherein the process may be carried out. However, it will bereadily apparent that this particular embodiment may be varied withoutdeparting from the scope of this invention.

Referring now to the drawing, there is shown a storage hopper 5 for thedouble fluoride salt, which is fed via line 11, gravimetric feeder '12,and line 13 into pulverizer I and the gravimetric feeders may beconventional equipment. Pulverizer 2 may also be any such equipmentwhich will pulverize or comminute the salt feed to an average particlesize of less than about mesh, preferable about 100 to 325 mesh.

The pulverized double fluoride salt and the diluent alkali metal halidesalt, when employed, recovered from pulverizer 2 is passed via conduit17 and line \18 to hopper 7 where it accumulates as a heel such that thevacuum maintained in hopper 3 will not pull any gases or vapors throughthe retained bed of pulverized material. From hopper 7 the pulverizedsalt is fed via line 19 to hopper 3 where it is heated to a temperatureof about 100 to 400 C., preferably about to 300 C., while the gases andvapors in hopper -3 are evacuated via line 20 to maintain substantiallyvacuum conditions in this hopper. In this step the waterand any absorbedgases are removed from the pulverized salt feed.

The dehydrated pulverized double fluoride salt is discharged from hopper3 via line 21 into gravimetn'c feeder 8, from where it passes via line27 into extruder 4. The extruder forces the pulverized material througha die plate to produce dry powdery pellets. The size of the pellets willbe determined by the particular dievplate employed and the amount ofcompaction obtained. For practical purposes, however, the pellets willhave an outside diameter of about /s to /2 inch and a length of about Ato 1 inch, although these sizes are not critical.' The salt pellets aretransported through barrel 23 of extruder 4 to reaction vessel 1. Itwill be understood that the reactor may be of conventional design.However, in order to more fully illustrate the invention, a conicalreaction vessel 1 is shown in the drawing. The reaction vessel isinternally lined with nickel or a suitable non-alloying material, and is18 inches deep with an internal diameter of 16 inches at top and aninternal diameter of 12 inches at the bottom. A nickel stillwell 24,having an internal diameter of 0.5 inch, extends through the reactorvessel wall 12 inches from the bottom of the reactor, and is positionedin a downward direction, parallel and against thereactor wall to a depthof 5 inches. Reaction vessel 1 is also provided with stirrer 9 which isof pitched blade design but may also be of any conventional design. As

shown in the drawing, reaction vessel 1 is positioned in reaction mediumneed be employed. Other methods of heating reaction vesselrl such asdirect heating may be utilized. The materials employed in the salt bathfurnace comprise sodium chloride, potassium chloride, lithium chloride,barium chloride, sodium fluoride, potassium fluoride, lithium fluorineand mixtures thereof.

, The molten reducing agent will be metered into the top of reactionvessel 1 via line 25. In accordance with another feature of theinvention, an inert gas atmosphere of about 1 to pe i.g. is maintainedin the reactor, at all times. Neon, ar on, etc. and mixtures of theseand other inert gases may be employed for this purpose. The inert gas ispassed into reaction vessel 1 via line 26.

In carrying out the process of the invention the pulverized doublefluoride salt, either alone or in admixture with the aforementionedinert salt diluent, is fed continuously in controlled amounts to areaction zone concurrently with a flow of molten reducing agent, e.g.sodium. The reaction product mixture which comprises finely dividedheavymetal particles is maintained under continuous agitation byrotating stirrer 9 at about 70 to 750 rpm. and is continuously withdrawnfrom the reaction zone via line 24 for separation of the desired metalproduct from the by-product salts.

Referring again to hopper 3, sufficient pulverized salt or salt mixturebed will be maintained in the hopper so that no air or other gas vaporswill gain entrance by passing through the bed. Since this same conditionexists in hopper 7, the evacuated space within hopper 3 can bemaintained at as low a vacuum as is necessary. In addition, it will beunderstood that both hoppers may be equipped with such conventionaldevices as stirrer-s, bridge-breakers, etc. as is required in order tomaintain movement of the powdered salt or salt mixtures into theentrance port of their respective discharging devices. With reference todischarge line 24 in reaction vessel 1 it will be understood that anyeffective overflow spout may be employed. Tie discharge line ispreferably so situated and equipped with a bathed entrance so that thereaction product mixture entering its opening has been contacted withsuflicient reducing agent to minimize the amount of unrcacted doublefluoride salts withdrawn. The actual discharging can be effected eitherby maintaining a positive pressure, derived from the atmosphere of inertgas, above the liquidus level in the reactor or by utilizing the forceof gravity such as by positioning the terminal ending of the dischargepipe at a sufliciently lower level than the level of the liquidus.

The invention will be more fully understood by reference to thefollowing illustrative embodiments, which are carried out in theapparatus described in the drawing:

Example I K TaF which has been previously comminued and outgassed, ismetered gravimctrically at a rate of 3.46 lb./min. from the gravimetricfeeder ahead of the extruder. The extruder passes the powdered salt intothe reactor, heated at 980 C. Simultaneously with this stream ofcompacted salt, molten sodium is metered into the reactor at a llb./min. rate. Both materials are contacted with molten K? and NaF inwhich is suspended tantalum metal particles produced from previousoperations with agitation, and they react together to produce particlesof tantalum metal and molten KF and NaF. A proportionate quantity(volumewise) of the reaction product mixture of NaF, KP and Ta isdisplaced from the reactor via the stillwell and empties continuouslyinto a suitable receiver at a rate of 4.40 lbs/min. of slurry,containing 36% tantalum metal by weight.

Example Il K TaF and KCl are metered gravimetrically from separatemetering stations at a rate of 3.44 lbs/min. each. The streams arejoined at a single runner disc mill and comminuted, with some degree ofmixing occurring, to 10O mesh. This mill discharge material istransported, successively through a surge bin evacuation hopper heatedat 150 C. Here some weight is lost due to outgassing of water andresidual gases. The evacuation hopper contents are stirred continuouslyto effect good mixing and outgassing of its charge. A blended stream ofsalts is discharged into a surge bin. The rate of discharge from theevacuation hopper is regulated by a level controller. The material isemptied from the surge bin by another gravimetric feeder station at arate of 6.80 lbs/min. into an extruder. The extruder compacts and feedsthe salt compresses into the reactor, heated at 800 C. Simultaneously,molten sodium is metered at a rate of l lb./min. Contacting of reactantsby agitation results in the formation of very fine particles of tantalummetal suspended in a liquid mixture comprising molten KF, NaF and KCl.The reaction by-products overflow via a stillwell into a suitablereceiver at a rate of 7.8 lbs./ min. containing 20% Ta.

In accordance with another aspect of the invention, various metal alloysmay be prepared by this process. More specifically, mixtures of two ormore alkali metalheavy metal fluoride salts may be treated by thepresent method to produce alloys of the heavy metals. Thus, a mixture ofthe columbium and tantalum double fluoride salts may be advantageouslyemployed to prepare columbium-tantalum alloys of varying compositions.It is also possible to use the alkali metal salt in such a process, ifdesired. Other than utilizing mixtures of double fluoride salts as thefeed material, the process will be the same as described above. This ismore fully illustrated in the following embodiment:

Example 111 Instead of charging one of the metering stations with KCl aswas done in Example II, K CbF is charged and fed in exactly the samemanner at a rate of approximately 1.38 lbs/min. This joins a stream ofmetered KzTaFq (1.75 lbs/min.) and this mixed stream is furtherprocessed as described in Example II. The compressed outgassed salts areextruded into a reactor at 900 C., at a total rate of 3.04 lbs/min.which is 35% wt. Cb and 65% wt. Ta in composition. Simultaneously, 1lb./min. of molten sodium is metered into the reactor. Reduction ofthese metal fluoride salts occurs instantaneously at these conditionswhen contacted, by means of agitation, with sodium. The resultantslurry, consisting of particles of Cb-Ta metal and molten KF and NaFoverflows from the reactor into a receiver at a rate of 4.04 lbs./ min.

In accordance with one method of starting up the process of thisinvention, a portion of the double fluoride salt ormixtures of suchsalts may becharged to reactor 1, and then heated under vacuum to atemperature of about 300 C. or higher with stirring. An inert gas suchas argon is introduced into the. reactor to maintain an inert atmosphereof about 5 p.s.i.g. After the reactor has been heated to a temperatureof about 800 C., a substantially stoichiometric amount of molten sodiumis added to the reactor. The reactor is then continuously charged .withfresh reactants, with or without a salt diluent, to commence the desiredoperations. As set forth above, a liquidus of reaction products will bemaintained in reactor 1 to serve as the reaction medium.

While particular embodiments ofthis invention are shown above, theinvention is obviously subject to varia tion and modification withoutdeparting from its broader aspects. For example, the alkali metal-heavymetal fluoride salt feed material may be prepared in accordance with anyknown process. It will be understood,'therefore, that these and othermodifications may be employed within the scope of the foregoingdescription of the invention and the following claims.

What is claimed is:

l. A continuous method for producing a metal selected from the groupconsisting of columbium and tantalum from a double fluoride salt thereofhaving the formula R MF V wherein R is an alkali metal and M is theselected metal,

which comprises continuously and simultaneously feeding said doublefluoride salt, in'solid form, and a molten alkali metal reducing agentinto a reaction zone and into molten products of reaction between saiddouble fluoride salt and said reducing agent contained in said reactionzone, said molten products of reaction being maintained at a temperatureof about 200 to 1000 C., and continuously removing a portion of thereaction product mixture containing the selected metal from saidreaction zone.

2. The method of claim 1 wherein M is columbium.

3. The method of claim 1 wherein M is tantalum.

4. The method of claim 1 wherein R is potassium.

5. The method of claim 1 wherein said molten reducing agent is sodium. I

6. The method of claim 1 wherein said double fluoride salt is ground toan average particle size of less than about 100 mesh and degassed priorto being fed into the reaction zone.

7. The method of claim 1 wherein a mixture of tantalumandcolumbium-alkali metal fluoride salts is fed into the reaction zone toproduce columbium-tantalum alloys.

8. The method of claim 1 wherein an inert alkali metal References Citedin the file of this patent UNITED STATES PATENTS 2,607,674 Winter Aug.19, 1952 2,647,826 Jordan Aug. 4, 1953 2,905,550 Taylor et a1 Sept. 22,1959 FOREIGN PATENTS 762,541 Great Britain Nov. 28, 1956 791,121 GreatBritain Feb. 26, 1958

1. A CONTINUOUS METHOD FOR PRODUCING A METAL SELECTED FROM THE GROUPCONSISTING OF COLUMBIUM AND TANTALUM FROM A DOUBLE FLUORIDE SALT THEREOFHAVING THE FORMULA